Category: Animals

Why porcupine quills slide in with ease but come out with difficulty

By Ed Yong | December 11, 2012 8:00 am

A shorter version of this story appears at Nature News.

In August of this year, Allison Noles rushed her bulldog Bella Mae to the vet. The dog’s face looked like a pincushion, with some 500 spines protruding from her face, paws and body. The internet is littered with such pictures, of Bella Mae and other unfortunate dogs. To find them, just search for “porcupine quills”.

North American porcupines have around 30,000 quills on their backs. While it’s a myth that the quills can be shot out, they can certainly be rammed into the face of a would-be predator. Each one is tipped with microscopic backwards-facing barbs, which supposedly make it harder to pull the quills out once they’re stuck in. That explains why punctured pooches need trips to the vet to denude their faces.

But that’s not all the barbs do. Woo Kyung Cho from Harvard Medical School and Massachusetts Institute of Technology has found that the barbs also make it easier for the quills to impale flesh in the first place. “This is the only system with this dual functionality, where a single feature—the barbs—both reduces penetration force and increases pull-out force,” says Jeffrey Karp, who led the study.

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Pygmy mole crickets leap from water with spring-loaded oars on their legs

By Ed Yong | December 3, 2012 11:00 am

When Malcolm Burrows first heard the sound of a pygmy mole cricket leaping from water, he was enjoying a sandwich. Burrows, a zoologist from the University of Cambridge, was visiting Cape Town and had snuck out the back of the local zoology department to eat his lunch by a pond. “I heard sporadic thwacking noises coming from the water,” he says. “When I looked more closely I could see small black insects jumping repeatedly from the water and heading towards the bank.”

They were pygmy mole crickets, a group of tiny insects just a few millimetres long. Despite their name, they’re more grasshoppers than crickets, and are some of the most primitive members of this group. They’re found on every continent except Antarctica.

Pygmy mole crickets cannot fly, but they can certainly jump. Burrows collected some of the individuals from the pond, and took them back to the lab to film them with high-speed cameras. When they take off, they often spin head-over-tail, but what they lack in elegance they make up for in distance. They can jump over 1.4 metres, more than 280 times their own body length.

Doing this on land is one thing, but as Burrows saw at the pond, these insects can also jump from water. This ability serves them well—they live in burrows near to fresh water, which frequently flood. Their leaps send them back to terra firma, saving their lives.

Burrows found that these insects jump from water in a completely new way. Animals like pond-skaters and the basilisk lizard can walk on water by relying on surface tension—the tendency of the surface of water to resist an external force. But the mole cricket extends its hind legs so quickly that they break right through the surface.

As the legs move through the water, three pairs of flat paddles and two pairs of long spurs flare out from each one. These structures have a concave shape, much like an oar. As they flare out, they increase the surface area of the mole cricket’s leg by around 2.4 times, allowing it to push down on a much larger volume of water. And once the legs are fully extended, the paddles retract to reduce the drag on the airborne insect. From water, the mole crickets can only jump for 3 centimetres or so. That’s pathetic compared to their land-based attempts, but still more than 5 times their body length, and enough to save them from drowning.

When Burrows shone ultraviolet light onto the paddles, they glowed with a bright blue colour at their bases. That’s the signature of resilin, an incredibly elastic protein that powers the jumps and wingbeats of many insects. Its presence on the mole cricket suggests that the paddles and spurs are spring-loaded.

“It just shows what amazing things can be found close to where we live and work,” says Burrows. “Instead of spending time exploring the more exotic parts of South Africa, I spent most of my visit there essentially looking outside my back door.”

Reference: Burrows & Sutton. 2012. Pygmy mole crickets jump from water. Current Biology 22: R990

All photos and video by Malcolm Burrows

Enter the hyperparasites – wasps that lay eggs in wasps that lay eggs in caterpillars

By Ed Yong | November 27, 2012 5:00 pm

(Left by Nina Fatouros, centre by Hans Smid, right by Harald Süpfle)

A very hungry caterpillar munches on a cabbage leaf and sets off an alarm. The plant releases chemicals into the air, signalling that it is under attack. This alarm is intercepted by a wasp, which stings the caterpillar and implants it with eggs. When they hatch, the larval wasps devour their host from the inside, eventually bursting out to spin cocoons and transform into adults. The cabbage (and those around it) are saved, and the wasp—known as a parasitoid because of its fatal body-snatching habits—raises the next generation.

But that’s not the whole story.

Some parasitic wasps are “hyperparasitoids”—they target other parasitoid wasps. And they also track the cabbage’s alarm chemicals, so they can find infected caterpillars. When they do, they lay their eggs on any wasp grubs or pupae that they find. Their young devour the young of the other would-be parasites, in a tiered stack of body-snatching. It’s like a cross between the films Alien and Inception.

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Why are stabby mantis shrimps so much slower than punchy ones?

By Ed Yong | November 21, 2012 4:08 pm

Credit: Professor Roy Caldwell at UC Berkeley.

If you want to find an ocean animal that kills with speed, don’t look to sharks, swordfishes, or barracuda. Instead, try to find a mantis shrimp. These pugilistic relatives of crabs and lobsters attack other animals by rapidly unfurling a pair of arms held under their heads. One group of them—the smashers—have arms that end in heavily reinforced clubs, which can lash out with a top speed of 23 metres per second (50 miles per hour), and hit like a rifle bullet. These powerful hammers can shatter aquarium glass and crab shells alike.

Most research on mantis shrimps focuses on smashers, but these pugilists are in the minority. The majority are “spearers”, whose arms end in a row of fiendish spikes, rather than hard clubs. While the smashers actively search for prey to beat into submission, the spearers are ambush-hunters. They hide in burrows and wait to impale passing victims. They’re Loki to the smashers’ Thor.

Given their differing lifestyles, you might expect the spearers to be faster than the smashers. They rely on quick strikes to kill their prey, and they target fast victims like fish and shrimp rather than the tank-like, slow-moving crabs favoured by smashers. But surprisingly, Maya DeVries from the University of California, Berkeley, found that the fastest spearer strikes at just a quarter of the speed of the fastest smasher.

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Wormholes in old books preserve a history of insects

By Ed Yong | November 20, 2012 7:15 pm

Absence can speak volumes. The lack of sediment in a flat piece of ground—a track—can testify to the footstep of a dinosaur that once walked on it. The lack of minerals in a solid shell—a hole—can reveal the presence of parasite that was once trapped in it. The world’s museums are full of such “trace fossils”, but so are many of the world’s art galleries.

The image above is taken from a woodcut currently residing in Amsterdam’s Rijksmuseum. It was made by etching a pattern into a block of wood, so that the remaining raised edges could be dipped in ink and used to print an image. These woodcuts were the main way of illustrating European books between the 15th and 19th centuries, and were used for at least 7 million different titles.

But as you can see, the print is littered with tiny white holes. These are called wormholes, and inaccurately so—they’re actually the work of beetles. The adults laid their eggs in crevices within the trunks of trees. The grubs slowly bored their way through the wood, eventually transformed into adults, and burrowed their way out of their shelters. The artists who transformed the tree trunks into printing blocks also inherited the exit-holes of the adult beetles, which left small circles of empty whiteness when pressed onto pages.

The beetles only emerged a year or so after the blocks were carved. The holes they left must have been frustrating, but remaking them would have been expensive. So the blocks were kept and reused despite their defects, unless the beetles had really gone to town. The holes they left behind preserve a record of wood-boring beetles, across four centuries of European literature. These holes are trace fossils. They’re evidence of beetle behaviour that’s been printed into old pages, just as dinosaur tracks were printed into the earth.

Now, Blair Hedges from Pennsylvania State University has used these fossils to study the history of the beetles that made them.

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The deadliest sea snake is actually two look-alike species

By Ed Yong | November 20, 2012 9:00 am

Sea snakes have some of the most potent venoms of any snake, but most of the 60 or so species are docile, rare, or sparing with their venom. The beaked sea snake (Enhydrina schistosa) is an exception. It lives throughout Asia and Australasia, has a reputation for being aggressive, and swims in estuaries and lagoons where it often gets entangled in fishing nets. Unwary fishermen get injected with venom that’s more potent than a cobra’s or a rattlesnake’s. It’s perhaps unsurprising that this one species accounts for the vast majority of injuries and deaths from sea snake bites.

But this deadliest of sea snakes has a secret: it’s actually two sea snakes.

By analysing the beaked sea snake’s genes, Kanishka Ukuwela from the University of Adelaide has shown that the Asian individuals belong to a completely different branch of the sea snake family tree than the Australian ones. They are two species, which have evolved to look so identical that until now, everyone thought they were the same. They’re a fantastic new example of convergent evolution, when different species turn up at life’s party wearing the same clothes.

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The insect that hears like a human, with ears on its knees

By Ed Yong | November 15, 2012 2:00 pm

Every time you put on some music or listen to a speaker’s words, you are party to a miracle of biology – the ability to hear. Sounds are just waves of pressure, cascading through sparse molecules of air. Your ears can not only detect these oscillations, but decode them to reveal a Bach sonata, a laughing friend, or a honking car.

This happens in three steps. First: capture. The sound waves pass through the bits of your ear you can actually see, and vibrate a membrane, stretched taut across your ear canal. This is the tympanum, or more evocatively, the eardrum. On the other side, the eardrum connects to three tiny well-named bones—the hammer, anvil and stirrup—which link the air-filled outer ear with the fluid-filled inner ear.

The bones perform the second-step: convert and amplify. They transmit all the pressure from the relatively wide eardrum into the much tinier tip of the stirrup, transforming large but faint air-borne vibrations into small but strong fluid-borne ones.

These vibrations enter the inner ear, which looks like a French whisk poking out of a snail shell. Ignore the whisk for now – the shell is the cochlea, a rolled-up tube that’s filled with fluid and lined with sensitive hair cells. These perform the third step: frequency analysis. Each cell responds to different frequencies, and are neatly aligned so that the low-frequency ones are at one end of the tube and the high-frequency ones at another. They’re like a reverse piano keyboard that senses rather than plays. The signals from these cells are passed to the auditory nerve and decoded in the brain. And voila – we hear something.

All mammal ears work in the same way: capture sound; convert and amplify; and analyse frequencies. But good adaptation are rarely wasted on just one part of the tree of life. Different branches often evolve similar solutions to life’s problems. And that’s why, in the rainforests of South America, a katydid—a relative of crickets—hears using the same three-step method that we use, but with ears that are found on its knees.

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MORE ABOUT: ear, hearing, katydid, knee

Corals summon gardening gobies to clean up toxic seaweed

By Ed Yong | November 9, 2012 9:00 am

For corals, gardening’s a matter of life and death. Corals compete with algal seaweeds for space, and many types of seaweed release chemicals that are toxic to corals, act as carriers for coral diseases and boost the growth of dangerous microbes. These dangers require close contact—the seaweed poisons won’t diffuse through the water, so they need to be applied to the corals directly. And that gives the corals an opportunity to save themselves. When they sense encroaching seaweed, they call for help.

Danielle Dixson and Mark Hay from the Georgia Institute of Technology have found that when Acropora corals detect the chemical signatures of seaweed, they release an odour that summons two gardeners – the broad-barred goby and redhead goby. These small fish save the corals by eating the toxic competitors. In return, one of them stores the seaweed poisons in its own flesh, becoming better defended against its own enemies.

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Fairy wrens teach secret passwords to their unborn chicks to tell them apart from cuckoo impostors

By Ed Yong | November 8, 2012 12:00 pm

In Australia, a pair of superb fairy-wrens return to their nest with food for their newborn chick. As they arrive, the chick makes its begging call. It’s hard to see in the darkness of the domed nest, but the parents know that something isn’t right. Whatever’s in their nest, it’s not their chick. It doesn’t’ know the secret password. They abandon it, flying off to start a new nest and a new family somewhere else.

It was a good call. The bird in their nest was a Horsfield’s bronze-cuckoo. These birds are “brood parasites” – they lay their eggs in those of other birds, passing on their parenting duties to some unwitting surrogates. The bronze-cuckoo egg looks very much like a fairy-wren egg, although it tends to hatch earlier. The cuckoo chick then ejects its foster siblings from the nest, so it can monopolise its foster parents’ attention.

But fairy-wrens have a way of telling their chicks apart from cuckoos. Diane Colombelli-Negrel from Flinders University in Australia has shown that mothers sing a special tune to their eggs before they’ve hatched. This “incubation call” contains a special note that acts like a familial password. The embryonic chicks learn it, and when they hatch, they incorporate it into their begging calls. Horsfield’s bronze-cuckoos lay their eggs too late in the breeding cycle for their chicks to pick up the same notes. They can’t learn the password in time, and their identities can be rumbled.

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Crocodile faces are more sensitive than human fingertips

By Ed Yong | November 8, 2012 8:07 am

Of all the adjectives you could use to describe a crocodile’s face, “sensitive” might not be an obvious one. But their huge jaws, pointed teeth and armoured scales belie a surprising secret. Their faces, and possibly their entire bodies, are covered with tiny bumps that are far more sensitive than our own fingertips.

The bumps are obvious if you look carefully. Each one is a small dome, barely a millimetre wide, surrounded by a groove. There are around 4,000 of them on an alligator’s jaws and inside its mouth. Crocodiles and gharials also have the bumps on virtually every scale of their bodies, giving a total of around 9,000. (All of these animals are called crocodilians.)

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